Oracle Databases on Raw Devices

Use

You can operate an Oracle database on raw devices. This means that the Oracle database management system avoids the file management of the UNIX system and instead writes data directly to a disk partition. Therefore, the partition is used as a raw device and does not contain a file system. This type of storage improves the speed of data access, but requires its own file management.

The BR*Tools support raw devices:

·        Raw Devices and BR*Tools

·        Raw Devices with BRBACKUP and BRRESTORE.

Raw devices are only used with the UNIX operating system, not with Windows NT.

Features

There are the following advantages and disadvantages when using raw devices.

Advantages

Working with raw devices improves performance for the following reasons:

·        Since the usual buffer cache for a file system is not needed, faster data access is possible and less main memory is required.

·        You do not have to administer a file system.

·        Since no management information has to be stored on the disk, less disk space is required.

·        Since the accesses do not have to be synchronized and the management information does not have to be recorded, the load on the CPU is reduced.

Disadvantages

Working with raw devices makes administration more difficult for the following reasons:

·        There is no description of the files residing on the raw devices in the system.

·        The configuration of the storage space is inflexible because only one database file is permitted for each raw device (and therefore for each partition). The sizes of the individual partitions must be adjusted to the sizes of the database files. This makes later relocation of the database files to other partitions more difficult.

·        It is possible to save raw devices with the dd command, but be aware of the disadvantages (for example, no end-of-media handling).